1. Field of the Invention
The invention relates generally to an apparatus for generating electrical power in a downhole well bore. More particularly, the invention relates to a fluid-driven alternator that includes an internal impeller.
The alternator is located downhole within a drilling string and is typically used to generate electrical power near the drill-bit in an oil well, gas well or the like. Mud, or drilling fluid, is circulated through the well bore as part of the drilling process and this flow is used to drive the alternator. The generated power is used, for example, to operate a downhole measurement-while-drilling (MWD) tool. MWD tools acquire drilling-related data (e.g., pressure, temperature, orientation, etc.) from sensors near the drill bit at the bottom of the well bore and transmit the data to the surface.
2. Description of the Related Art
There are several known ways to provide the electric power necessary to operate MWD tools.
One conventional manner for providing electricity to downhole MWD tools is through a power cable connected from the surface through the drill string to the tool. This method suffers from the disadvantage of causing significantly increased rig time to be consumed because the cable must be retrieved from the well to enable each new section of drill pipe to be added and then re-installed.
Another conventional manner for providing electricity to downhole MWD tools is through the use of high-temperature batteries, typically Lithium Thionyl Chloride batteries. However, these batteries are expensive to build, difficult (and dangerous) to deploy logistically, and troublesome to dispose of when depleted. Furthermore, batteries have a short usable life, and the entire MWD tool must be removed in order to replace depleted batteries. Removing the MWD tool for the sole purpose of replacing batteries is very time consuming and costly.
A third conventional manner for providing electricity to downhole MWD tools is through the use of a mud-driven alternator assembly. Known alternators operate with external impeller blades that extend into the normal annular mud flow path around the MWD tool assembly. The mud flow rotates the external impellers, which drive the alternator to continuously generate power. This configuration is acceptable for a non-retrievable MWD tool; however, it is not suitable for a retrievable MWD tool where the complete tool must be removed through the drill string without getting caught and without damaging the assembly. The external impeller blades are unprotected and increase the outer diameter of the alternator assembly, thereby making it difficult to withdraw the alternator through a restricted section of the drill string.
It is a general object of the present invention to provide an impeller device of a fluid-driven alternator that overcomes the disadvantages of the conventional power-supplying devices.
It is another object of the present invention to provide an impeller device of a fluid-driven alternator that allows the assembly to be retrieved from within the drill string without getting caught or being damaged.
It is still another object of the present invention to provide an impeller device of a fluid-driven alternator where the impeller device has an internal impeller.
It is yet another object of the present invention to provide an impeller device of a fluid-driven alternator also having a flow diverter to divert the fluid flow to the internal impeller of the impeller device.
It is another object of the present invention to provide an impeller device of a fluid-driven alternator also having a flow diverter to divert the fluid flow to an internal impeller of the impeller device, where the upper speed (rpm) of the internal impeller is reduced.
In accordance with the objects described above, one aspect of the present invention includes a housing, an internal impeller rotatably mounted in the housing, a stator mounted within the housing, and a rotor rotatably mounted in the housing and coupled to the impeller. The housing includes at least one entrance opening and at least one exit opening, and the impeller includes at least one impeller blade and a drive shaft. Fluid flowing through the housing rotates the impeller thereby rotating the rotor.
In another aspect of the present invention, the alternator described above further includes a flow diverter on an exterior of the housing and located between the entrance and exit openings. The flow diverter restricts fluid flow in a flow path along the housing and directs at least some of the flowing fluid into the entrance opening.
In yet another aspect of the present invention, the flow diverter described above is molded onto the housing, includes at least one diverter ring made of an elastomer material and is capable of flexing at a predetermined rate of fluid flow to reduce the restriction.
In still another aspect of the present invention, the flow diverter described above is removably attached to the housing, includes at least one diverter ring made of an elastomer material and is capable of flexing at a predetermined rate of fluid flow to reduce the restriction.
In still another aspect of the present invention, the flow diverter described above is removably attached to the housing, includes a plurality of diverter rings made of an elastomer material and is capable of flexing at a predetermined rate of fluid flow to reduce the restriction.
In another aspect of the present invention, a fluid-driven alternator for use in a downhole well bore having fluid flowing therethrough includes a housing containing an upper bearing assembly, a lower bearing assembly and an impeller. The impeller has an upper end, a lower end and at least one impeller blade, and is rotatably attached at the upper end to the upper bearing assembly and at the lower end to the lower bearing assembly. The impeller is also coupled at one end to a rotor, which is part of an alternator assembly. The alternator assembly also includes an alternator stator. The housing has at least one entrance opening near the upper end of the impeller and at least one exit opening near the lower end of the impeller. Fluid enters the housing through the entrance opening, flows over the impeller blade, and exits the housing through the exit opening. The fluid flowing over the impeller blade rotates the impeller in the upper and lower bearing assemblies, thereby rotating the rotor of the alternator assembly.
According to yet another aspect of the present invention, the alternator further includes a flow diverter on an exterior of the housing. The flow diverter restricts fluid flow around the housing and diverts at least some of the fluid flow into the housing through the entrance opening.
According to still another aspect of the present invention, the flow diverter includes a plurality of flexible rings that deflect as a force of the fluid flowing on the diverter rings increases with an increase in a flow of the fluid, and the fluid flowing into the entrance opening of the housing tends to flatten off at the upper end of a fluid flow range for the impeller.
According to another aspect of the present invention, a fluid-driven alternator includes an internal impeller, housing means for housing and rotatably mounting the internal impeller, and alternator means, including a rotor and a stator, coupled to the internal impeller for generating electricity. The internal impeller is rotated by fluid flowing through the housing means and in turn rotates the rotor.
In yet another aspect of the present invention, the alternator further includes flow diverter means for diverting fluid flow into the housing means.
These and other aspects, objects, and features of the present invention will become apparent from the following detailed description of the preferred embodiments of the present invention, read in conjunction with reference to the accompanying drawings.